Millions of people who register to vote are unaware their personal details are being sold to cold-calling sales companies who collate it, then sell it on.

This practice is legal but consumer groups and councils would like to see it banned.

The law was changed under the previous Labour government in 2002, when direct marketing companies were given the right to buya copies of the electoral roll from Local Authorities. As a result cold calling is thriving, and it is estimated that 1.5 billion unsolicited calls were made last year.

Local Councils charge around £1,900 from a sale but officials believe that the fee does not even cover the cost of administration. It is thought direct marketing companies earn millions from the trade.

Local Government Association representative, Richard Kemp said:

“Town halls hugely resent having to pass the electoral roll to direct marketing companies.

“This process undermines democracy, ­dissuades people from voting and gives ­people the impression that the council is profiting from selling their personal information.”

A survey by consumer magazine Which? says that it is common for homes to receive more than 100 unsolicited calls a year, with 7% saying they received about five calls a week.

Jane Pierson, of Which?, said:

“Our readers regard cold-calling as an invasion of privacy but it is clear that some sales companies are coming to rely on it heavily.

“We believe that it’s time this whole area was closely looked into.”

Kathryn Powell, of campaign group Call Prevention Registry, said:

“Most people fill in their electoral roll forms in good faith. They can be fined £200 and forfeit their right to vote if they don’t. They aren’t aware that there is a little box at the bottom that you can tick to keep your name off the list when it’s sold.

“One internet firm also offers to supply birth, death and marriage details as well as the householder’s occupation and how much they paid.

“People just don’t realise how much can be found out about their personal lives at the flick of a switch. It’s a frightening prospect.”